sliplogin(8)

NAME

sliplogin - attach a serial line network interface

SYNOPSIS

sliplogin [loginname [device]]

DESCRIPTION

The sliplogin utility is used to turn the terminal line on

standard input
(or device) into a Serial Line IP (SLIP) link to a remote

host. To do
this, the program searches the file /etc/sliphome/slip.hosts

for an entry
matching loginname (which defaults to the current login name

if omitted).
If a matching entry is found, the line is configured appro

priately for
slip (8-bit transparent i/o) and converted to SLIP line dis

cipline using
the optional line discipline parameters.

The optional line discipline parameters consist of one or

more of the
following; `normal', `compress', `noicmp', or `autocomp'

which correspond
respectively to `use normal line discipline' (no header com

pression),
`enable VJ header compression', `throw away ICMP packets',

and `auto
enable VJ header compression' (only if the remote end of the

link also
supports it).

Then a shell script is invoked to initialize the slip inter

face with the
appropriate local and remote IP address, netmask, etc.

The usual initialization script is /etc/sliphome/slip.login

but, if particular hosts need special initialization, the file
/etc/sliphome/slip.login.loginname will be executed instead

if it exists.
The script is invoked with the parameters

slipunit The unit number of the slip interface assigned to

this line.

E.g., 0 for sl0.

speed The speed of the line.

args The arguments from the /etc/sliphome/slip.hosts

entry, in order

starting with loginname.

Only the super-user may attach a network interface. The in

terface is
automatically detached when the other end hangs up or the

sliplogin process dies. If the kernel slip module has been configured

for it, all
routes through that interface will also disappear at the

same time. If
there is other processing a site would like done on hangup,

the file
/etc/sliphome/slip.logout or

/etc/sliphome/slip.logout.loginname is executed if it exists. It is given the same arguments as the

login script.

Format of /etc/sliphome/slip.hosts

Comments (lines starting with a `#') and blank lines (or

started with
space) are ignored. Other lines must start with a loginname

but the
remaining arguments can be whatever is appropriate for the

slip.login
file that will be executed for that name. Arguments are

separated by
white space and follow normal sh(1) quoting conventions

(however,
loginname cannot be quoted). Usually, lines have the form

loginname local-address remote-address netmask opt

args

where local-address and remote-address are the IP host names

or addresses
of the local and remote ends of the slip line and netmask is

the appropriate IP netmask. These arguments are passed directly to

ifconfig(8).
Opt-args are optional arguments used to configure the line.

FreeBSD Additions

An additional SLIP configuration file (if present) is
/etc/sliphome/slip.slparms. If particular hosts need dif

ferent configurations, the file /etc/sliphome/slip.slparms.loginname will

be parsed
instead if it exists.

Format of /etc/sliphome/slip.slparms*

Comments (lines starting with a `#') and blank lines (or

started with
space) are ignored. This file contains from one to three

numeric parameters separated with spaces, in order: keepalive, outfill and

slunit.

keepalive Set SLIP "keep alive" timeout in seconds. If

FRAME_END is not

received in this amount of time, sliplogin closes

the line and
exits. The default value is no timeout (zero).

outfill Set SLIP "out fill" timeout in seconds. It

forces at least

one FRAME_END to be sent during this time period,

which is
necessary for the "keep alive" timeout on the re

mote side.
The default value is no timeout (zero).

slunit Set the SLIP unit number directly. Use with cau

tion, because

no check is made for two interfaces with same

number. By
default sliplogin dynamically assigns the unit

number.

If latter two parameters are omitted, they will not affect

the corresponding SLIP configuration. If any of first two parameters

is equal to
zero, it will not affect the corresponding SLIP configura

tion.

FILES

/etc/sliphome/slip.hosts

list of host login names and parameters.

/etc/sliphome/slip.login

script executed when a connection is made.

/etc/sliphome/slip.login.loginname

script executed when a connection is made by

loginname.

/etc/sliphome/slip.logout

script executed when a connection is lost.

/etc/sliphome/slip.logout.loginname

script executed when a connection is lost by

loginname.

/etc/sliphome/slip.slparms

extra parameters file.

/etc/sliphome/slip.slparms.loginname

extra parameters file for loginname.

/var/run/ttyXn.if

contains the name of the network interface used by

the sliplogin
process on ttyXn.

/var/run/slX.pid

contains the PID of the sliplogin process which is

using interface slX.

EXAMPLES

The normal use of sliplogin is to create a /etc/passwd entry

for each
legal, remote slip site with sliplogin as the shell for that

entry.
E.g.,

Sfoo:ikhuy6:2010:1:slip line to foo:/tmp:/usr/sbin/sliplogin

(Our convention is to name the account used by remote host

hostname as
Shostname.) Then an entry is added to slip.hosts that looks

like:

Sfoo `hostname` foo netmask

where `hostname` will be evaluated by sh(1) to the local

host name and
netmask is the local host IP netmask.

Note that sliplogin must be setuid to root and, while not a

security
hole, moral defectives can use it to place terminal lines in

an unusable
state and/or deny access to legitimate users of a remote

slip line. To
prevent this, sliplogin is installed as user root, group

network and mode
4550 so that only members of group network may run

sliplogin. The system
administrator should make sure that all legitimate users are

a member of
the correct group.

DIAGNOSTICS

The sliplogin utility logs various information to the system

log daemon,
syslogd(8), with a facility code of daemon. The messages

are listed
here, grouped by severity level.

Error Severity
ioctl (TCGETS): reason

A TCGETS ioctl() to get the line parameters failed.

ioctl (TCSETS): reason

A TCSETS ioctl() to set the line parameters failed.

/etc/sliphome/slip.hosts: reason

The /etc/sliphome/slip.hosts file could not be

opened.

access denied for user

No entry for user was found in

/etc/sliphome/slip.hosts.

Notice Severity
attaching slip unit unit for loginname

SLIP unit unit was successfully attached.

SEE ALSO

slattach(8), syslogd(8)

/usr/share/examples/sliplogin

HISTORY

The sliplogin utility appeared in 4.3BSD-Reno.

BSD January 5, 1994

BSD